1. Technical Field
The present invention relates to an electronic device, a radio communication terminal, and data transmission method. Specifically, it is suitable for an electronic device and a radio communication terminal having two parts close to each other as a clamshell type cellular telephone unit, in which data transmission is performed between the parts.
2. Related Art
In regard to a cellular telephone in recent years, the efforts to make higher the resolution of a liquid crystal display device incorporated in the cellular telephone have been made to enable finer display of a still image shot by a digital camera and a moving image as well as still images of a character, a graphic symbol, etc. In parallel to this, the amount of data communicated between a digital camera and a liquid crystal display device has been increased. As a result, it has been proposed to use a high-speed transfer method, LVDS (Low Voltage Differential Signaling), for connections of a display unit and an imaging device.
Also, as for a cellular telephone in recent years, a clamshell structure that enables the cellular telephone to be folded has been adopted to upsize a display unit and prevent an operation button from being pushed accidentally when the cellular telephone is carried, without loss of portability of cellular telephones. According to the clamshell structure, a first body part incorporating a control part that is mainly responsible for an external radio communication function of a cellular telephone and a second body part equipped with a display unit are coupled through a hinge, and the first and second body parts can be opened and closed using the hinge.
On the other hand, in the situation where the resolution of a display unit incorporated in a cellular telephone is made higher increasingly, the multiple pin technique has to be applied to a flexible wiring board to send a signal to the display unit for the purpose of sending image data or the like to the display unit by wire at a high bit rate. In the case of a cellular telephone of the clamshell structure, when data transmission between the first and second body parts is performed by wire, it is required to engage a flexible wiring board to which the multiple pin technique is applied with the hinge, which makes the structure of the hinge more complicated and the mounting process more troublesome. Therefore, a method of performing data transmission between the first and second body parts by internal radio communication has been proposed, by which internal radio communication antennas are provided on the first and second body parts respectively instead of the flexible wiring board.
For example, JP-A-2002-171321 discloses a mobile radio terminal including a radio unit and an operation unit, which can be separated from each other, for radio communications with a base station, and a method of sending/receiving sound and image data, by which sound and image data are sent/received by electrically connecting the radio and operation units through connectors included in the units respectively, in the condition where the units are integrated, and sound and image data are sent/received by Blue tooth radio communication between the units in the condition where the units are separated.
Now, there are two detection methods for digital radio communication, synchronous detection and asynchronous detection. The asynchronous detection includes delay detection and envelope detection, which is inferior in bit error rate characteristic to synchronous detection. On the other hand, with the synchronous detection, a sign can be detected and discriminated using as a reference a carrier reproduced based on received signals, as disclosed in e.g. JP-A-05-110609.
However, the synchronous detection has an unsolved problem such that it requires a circuit to reproduce a carrier, which increases the circuit scale and power consumption.
In the digital radio communication system, phase modulation such as BPSK or QPSK is often used. The following procedures have been devised. That is, on the receiving side, a receiving mixer converts the phase-modulated transmission data in frequency using a local oscillator output into a received base band signal. The received base band signal is supplied to a low-pass filter to remove the noise thereof and then binarized by a limiter, and supplied to a base band processing part. However, in this case, when the phase of the received local oscillator output, which is multiplied in the receiving mixer, is coincident with that of the carrier on the transmission side, the received base band signal resulting from filtering by the low-pass filter is maximized in its amplitude as shown in FIG. 8A. The received base band signal is binarized in the limiter into a binarized base band signal. The binarized base band signal is made a normal base band signal as shown in FIG. 8B. In the case where the phase of the received local oscillator output differs from that of the sent carrier by 45°, the received base band signal resulting from filtering by the low-pass filter is somewhat reduced in amplitude as shown in FIG. 9A, whereas the binarized base band signal resulting from binarization of this post-filtering signal by the limiter allows the reproduction of substantially normal base band signal, as shown in FIG. 9B.
However, in the case where the phase of the received local oscillator output differs from that of the sent carrier by 90°, the received base band signal resulting from filtering by the low-pass filter is remarkably reduced in amplitude as shown in FIG. 10A. The binarized base band signal resulting from binarization of this post-filtering signal by the limiter is in a condition such that it is hard to discriminate between a signal and a noise, as shown in FIG. 10B.
On this account, as a method of adjusting the phase of the received local oscillator output in the past, there have been used a method of maximizing the received base band signal by an analog feed-back system, a method of using a digital feed-back system with a multi-bit A/D converter and a matched filter to monitor, by which the amplitude information is monitored by a digital control part to adjust the phase, etc.
However, the analog feed-back system has an unsolved problem such that fine adjustments of a time constant of a circuit, etc. are difficult, and a filter circuit for feed back and others increase the cost and power consumption.
On the other hand, the digital feed-back system has an unsolved problem such that it is high in control flexibility, but use of the multi-bit A/D converter inevitably increases the cost and power consumption. Incidentally, there is an alternative method, by which a limiter amplifier or the like is used and a one-bit A/D converter digitalizes only the phase information. However, such method has an unsolved problem such that it is required to additionally provide some means of detecting the amplitude level of a received base band signal, which inevitably increases the cost and power consumption.